Largest freshwater fish ever caught in Cambodia

A fisherman in northern Cambodia has hooked what researchers say is the world’s largest freshwater fish — a giant stingray about which scientists know relatively little.

The 42-year-old fisherman caught the 661-pound fish – which was about 13 feet long – near a remote island in the Mekong in the Stung Treng area. A team of scientists from the Wonders of Mekong research project helped tag, measure and weigh the ray before releasing it back into the river. The research group believes it was healthy when released and expects it to survive.

The tag, which emits an audible signal, will allow researchers to track the fish’s movements and, they hope, learn more about the behavior of its species in the Mekong.

The catch “shows how little we know about many of these giant freshwater fish,” said Zeb Hogan, a fish biologist at the University of Nevada. “They have a fish that is now the record holder for the world’s largest freshwater fish, and we know little about it.”

Fisherman Moul Thun hooked and lined the giant ray on the evening of June 13 and then contacted the researchers the next morning.

Wonders of Mekong researchers have already been to northern Cambodia to install underwater receivers as part of a project to track migratory fish in the river.

“It’s a particularly healthy section of the river with a lot of deep pools – pools up to 300 feet deep,” said Hogan, who is also the host of National Geographic’s television series Monster Fish. “We began to focus on this area as a stretch of river that is particularly important for biodiversity and fisheries, and as a last resort for these large species.”

For several months, the research group has been in contact with local fishermen, asking them to get in touch if they land a significant catch. The group has assisted with two other large releases of giant freshwater rays in recent months. The fisherman who caught the record ray was paid for his catch at market price.

“It works because the fish isn’t a prized food fish,” Hogan said.

Hogan said little is known about the giant freshwater stingray. The creature has a mouth about “the size of a banana” with no teeth but with “gripping pads” used to crush prey.

“They are on the bottom and find shrimp, mollusks and small fish. You can suck them up and mash them with that banana-shaped mouth,” Hogan said.

Wonders of the Mekong team members, Cambodian fisheries officials and villagers took photos with the giant freshwater stingray.
Wonders of the Mekong team members, Cambodian fisheries officials and villagers took photos with the giant freshwater stingray.Chhut Chheana / Wonders of the Mekong

Fishermen have reported three catches of female stingrays in the area in the past two months, Hogan said. The scientists suspect that the site could be an important seasonal gathering place for giant freshwater stingrays and could serve as a breeding ground for juveniles.

The research group plans to tag and track a few hundred large fish in the Mekong to better understand fish migrations and local habitat in Cambodia’s upper Mekong.

“Right where these stingrays were caught, there is potential for hydroelectric power development,” Hogan said. “We want to understand the importance of this area before potentially unsustainable development occurs.”

Hogan said the Cambodian government has expressed an interest in developing a conservation plan for the giant freshwater stingrays.

The Upper Mekong is also a habitat for Mekong giant catfish and other species of large freshwater fish.

Globally, “most of these big fish species are in trouble, their populations are declining. The Chinese paddlefish was declared extinct in 2020,” Hogan said. “We must do more to protect these freshwater habitats.”

The former world record fish – a 646-pound Mekong giant catfish – was also caught in the Mekong River in Thailand in 2005.

There are other, larger recorded catches of fish that live in both freshwater and saltwater, such as B. the beluga sturgeon.

“This is the record for the largest fish to live its entire life in freshwater,” Hogan said of the recently caught ray.